Oliver Holmes in Jerusalem

Activists who attempted to sail a fishing boat carrying aid to Gaza but were intercepted by the Israeli navy have complained of violence during a boarding operation.

(Israel has been hijacking these countless boats on high sea since 2014, after its savage pre-emptive on Gaza that killed over 1,700 and maimed triple that numbers)

Israel held the 20 foreigners and the boat after they arrived several dozen miles off the coast of Gaza on Sunday and were in the process of releasing and deporting the crew, the group said.

Most of those on board Al Awda, which means The Return in Arabic, were held in prison, while two Israelis on the vessel were released on bail.

Freedom Flotilla said the Norwegian-flagged boat had been surrounded by “12 military vessels with hundreds of armed soldiers”.

“Some participants were repeatedly tasered, including in the head. Others were punched or had their head beaten against a wall by IOF soldiers. Zip-cuffs were used in a manner which cut off circulation,” Freedom Flotilla said, referring to Israeli troops as Israel Occupation Forces.

The account appeared to conflict with that of the Israeli military on Sunday, which said the boat was “monitored and was intercepted” and “the activity ended without exceptional events”.

On Thursday, the military said its forces “used proportional force in order to constrain the provocateurs on board the ship”. It did not say how many activists it had deported or if any remained in custody.

Al Awda was carrying €13,000 (£11,500) worth of medical supplies for Gaza, which were transferred to the enclave by Israeli authorities after the boat was confiscated.

Among those deported was Australian Chris Graham, editor of the independent news website New Matilda. Another crew member, Swee Ang, a British orthopaedic surgeon who helped to establish the charity Medical Aid for Palestinians, said she had also arrived back in the UK.

The boat’s captain accused Israeli authorities of illegally boarding the vessel in international waters. “We were closer to Egypt than Israel,” Herman Reksten said when he returned to Norway. “I still have a headache from being hit in prison.”

Mike Treen, an activist and union leader from New Zealand, said on his return to Auckland that Israeli soldiers had worn balaclavas as the activists linked arms. “They just started tasering us, beating and tasering us to get out the way,” he said, adding that many had had their belongings confiscated.

Israel imposes a naval blockade on Gaza and has in the past blocked ships from reaching it shores, most infamously in 2010 when it launched an operation that killed 10 people.

Torstein Dahle, head of Ship to Gaza Norway, which organised the mission, said the idea was in part to raise awareness for Gaza’s fishermen who face attacks from Israeli forces and are restricted to six nautical miles from the coast.

“The ultimate step is an attempt to break the blockade and its devastating effects,” he said by phone from Norway.

Dahle said Mikkel Gruner, a Danish citizen who lives in Norway, was badly beaten. “He was hit by blows. They destroyed his glasses,” he said.

The crew had been told the boat would be confiscated as the Israelis feared it could be used by Hamas, Dahle said. “But we have no connection with Hamas,” he said, adding that the ship sails at a speed of seven knots and would be useless as a military vessel.

A spokesman at Norway’s foreign ministry said the government had asked Israel “to clarify the circumstances around the seizure of the vessel and the legal basis for the intervention”.

Gaza is home to 2 million Palestinians, mainly the descendants of refugees who fled or were driven out of what is now Israel around the time of its creation in 1948

A 10-year blockade by Israel and Egypt, coupled with economic restrictions imposed on Hamas by its political rivals in the West Bank, have all but destroyed the economy.

In recent weeks, Israel has tightened the blockade. On Thursday it banned fuel deliveries, which it said was in response to Palestinians flying kites carrying lit cans of petrol which have caused fires in Israel.

The “flaming kites” attacks began after several weeks of protests by Palestinians near the perimeter fence that were met by lethal force from Israeli snipers. More than 150 Palestinians, including children, medics and journalists, have been shot dead. Several thousand more have been shot in the legs.

The bloodshed has resulted in the most severe exchanges of fighting since a 2014 war, with Israel using airstrikes and Hamas mortar and rocket attacks. Last month, an Israeli soldier died after he was hit by Palestinian gunfire. (That news. But the 200 Palestinians killed by live bullets and the hundred handicapped, shot in the legs, are invisible body to mention)

The Gaza-based Al Mezan Center For Human Rights condemned the seizure of the boat and said it had drawn attention to the blockade, “a collective punishment, illegal under international law”.

A second boat, the Swedish-flagged Freedom, is due to approach Gaza in the coming days.

Agence France-Presse contributed to this report